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ABSTRACT Mariculture and recreational zones are expanding rapidly along the coast of Primorsky Krai in the Russian Far East, increasing the pressing need for monitoring of toxin-producing algae and seafood [...]

Oceanic high-nitrate, low-chlorophyll environments have been highlighted for potential large-scale iron fertilizations to help mitigate global climate change. Controversy surrounds these initiatives, both in the degree of carbon removal and magnitude of ecosystem impacts. Previous open ocean enrichment experiments have shown that iron additions stimulate growth of the toxigenic diatom genus Pseudonitzschia. Most Pseudonitzschia species in coastal waters produce the neurotoxin domoic acid (DA), with their blooms causing detrimental marine ecosystem impacts, but oceanic Pseudonitzschia species a re considered nontoxic. Here we demonstrate that the sparse oceanic Pseudonitzschia community at the high-nitrate, low-chlorophyll Ocean Station PAPA (50[degrees] N, 145[degrees] W) produces approximately 200 pg DA [L.sup.-1] in response to iron addition, that DA alters phytoplankton community structure to benefit Pseudonitzschia, and that oceanic cell isolates are toxic. Given the negative effects of DA in coastal food webs, these findings raise serious concern over the net benefit and sustainability of large-scale iron fertilizations. carbon sequestering | domoic acid | ocean iron fertilization | Pseudonitzschia | toxicity doi/10.1073/pnas.0910579107

In September 2004 a large, nearly monospecific diatom bloom of Pseudo-nitzschia euspidata off the coast of the state of Washington reached cell concentrations of 6.1 x [10.sup.6] cells [L.sup.-1] and produced maximum particulate domoic acid (pDA), dissolved domoic acid (dDA), and cellular domoic acid concentrations of 43 nmol [L.sup.-1], 4 nmol [L.sup.-1], and 63 pg [cell.sup.-1], respectively. This bloom co-dominated the phytoplankton assemblage with the euglenoid Eutreptiella sp. in the Juan de Fuca eddy region, a known initiation site for toxigenic Pseudo-nitzschia blooms. Two isolates of P. cuspidata collected during separate cruises produced domoic acid (DA) in culture. During the September 2004 survey, 84% of the stations (n = 98) had detectable Pseudo-nitzschia and 78% had detectable pDA. There were no significant correlations between either pDA or cellular DA and ambient concentrations of macronutrients; however, when considering only those stations where Pseudo-nitzschia was present, pDA was positively correlated with chlorophyll a and negatively correlated with temperature (p [less than or equal to] 0.01) at both 1- and 5-m depths. Correlations between cellular DA concentrations and total bacteria or cyanobacteria abundances were not significant. Variable ratios of pDA:dDA in the eddy region suggest that DA release was under cellular regulation by Pseudo-nitzschia. Stations where dissolved Fe concentrations were limiting (

The Juan de Fuca eddy is a toxic 'hot spot.' Domoic acid (DA) was detected in the eddy during each of six cruises over a 4-yr study, although Pseudo-nitzschia abundance and toxin concentrations were highly variable. During the September 2004 eddy bloom, Pseudo-nitzschia spp. exceeded 13 x [10.sup.6] cells [L.sup.-1], and particulate DA reached 80 nmol [L.sup.-1]. Of the >10 species of Pseudo-nitzschia identified in this region, those coincident with the most toxic blooms are P. cf. pseudodelicatissima, P. cuspidata, P. multiseries, and P. australis. However, the presence of any particular species could not be used as an indicator of toxicity because of the high level of variability in intracellular DA in field assemblages. Pseudo-nitzschia cells were typically associated with blooms of other diatom taxa but also were coincident with blooms of euglenoids and dinoflagellates in the eddy region. Pseudo-nitzschia always comprised

Iron is a bioactive trace element in seawater that regulates photosynthetic carbon dioxide drawdown and export from surface waters by phytoplankton in upward of 40% of the world's oceans. While autonomous sensor arrays are beginning to provide high-resolution data on temporal and spatial scales for some key oceanographic parameters, current analytical methods for iron are not amenable to autonomous platforms because of the need for user involvement and wet chemistry-based approaches. As a result, very large gaps remain in our understanding of iron distribution and chemistry in seawater. Here we present a straightforward nanostructure-based method to measure dissolved iron in natural seawater. The device comprises an iron-specific chelating biomolecule, desferrioxamine B (DFB), covalentiy immobilized on a mesoporous silica film. Changes in infrared spectral signatures of the immobilized DFB upon Fe(III) complexation provide an accurate and precise measure of iron on the surface of a chip exposed to seawater. The current system has a detection limit of ~50 pM for a 1-L sample at pH 1.7 and was used to measure dissolved iron in subarctic Pacific waters without interference from other elements in seawater. This technology provides a major step toward obtaining accurate iron measurements on autonomous research platforms.

Proteins with intrinsically disordered domains are implicated in a vast range of biological processes, especially in cell signaling and regulation. Having solved the quaternary structure of the folded domains in the tumor suppressor p53 by a multidisciplinary approach, we have now determined the average ensemble structure of the intrinsically disordered N-terminal transactivation domain (TAD) by using residual dipolar couplings (RDCs) from NMR spectroscopy and small-angle x-ray scattering (SAXS). Remarkably, not only were we able to measure RDCs of the isolated TAD, but we were also able to do so for the TAD in both the full-length tetrameric p53 protein and in its complex with a specific DNA response element. We determined the orientation of the TAD ensemble relative to the core domain, found that the TAD was stiffer in the proline-rich region (residues 64-92), which has a tendency to adopt a polyproline II (PPII) structure, and projected the TAD away from the core. We located the TAD in SAXS experiments on a complex between tetrameric p53 and four Taz2 domains that bind tightly to the TAD (residues 1-57) and acted as 'reporters.' The p53-Taz2 complex was an extended cross-shaped structure. The quality of the SAXS data enabled us to model the disordered termini and the folded domains in the complex with DNA. The core domains enveloped the response element in the center of the molecule, with the Taz2-bound TADs projecting outward from the core. hybrid methods | natively unfolded | protein | residual dipolar coupling | small-angle x-ray scattering

The chemical denaturant guanidine hydrochloride (GuHCI) is used to examine the unfolding transitions of PrP(super c) to study the intermediates in the equilibrium conditions. Analysis of NMR chemical shift and intensity changes indicates that there is persistent structure in the molecule well beyond the major cooperative unfolding transition.

Diatom blooms generated by the alleviation of iron limitation in high nitrate-low chlorophyll (HNLC) regions of the oceans often are composed of pennate diatoms of the genus Pseudo-nitzschia, many of which periodically produce the potent neurotoxin domoic acid. We show that toxigenic diatoms have an inducible high-affinity iron uptake capability that enables them to grow efficiently on iron complexed by strong organic ligands in seawater. This low-iron adaptive strategy requires copper and domoic acid, a copper chelator whose production increases sharply when both iron and copper are limiting. Addition of either domoic acid or copper to seawater improves the growth of Pseudo-nitzschia spp. on strongly complexed iron during deck incubation experiments with natural phytoplankton. Our findings indicate that domoic acid is a functional component of the unusual high-affinity iron acquisition system of these organisms. This system may help explain why Pseudo-nitzschia spp. are persistent seed populations in oceanic HNLC regions, as well as in some neritic regions. Our findings also indicate that in the absence of an adequate copper supply, iron-limited natural populations of Pseudo-nitzschia will become increasingly toxic.

Toxigenic pennate diatoms of the genus Pseudo-nitzschia produce domoic acid (DA), the neurotoxin linked to amnesic shellfish poisoning. We investigated how Fe and Cu affect growth and DA production by P. multiseries and P. australis clones isolated from Monterey Bay, California. Growth rates of these species could be inhibited by both Fe limitation (pFe 20.5, [mu] = 50% [[mu].sub.max]) and Cu toxicity (pCu 10.5, [mu] = 30-50% [[mu].sub.x]). The rate of DA production during the exponential phase was a significant inverse function of cellular growth rates (P < 0.02). Voltammetric measurements of dissolved DA-equivalents in short-term experiments indicated that the cellular production of DA increased from ~5 amol DA [cell.sup.-1] [h.sup.-1] under optimal growth conditions to ~40 amol DA [cell.sup.-1] [h.sup.-1] under Fe-deficient conditions and ~105 amol DA [cell.sup.-1] [h.sup.-1] under Cu-stressed conditions. The DA was released to the medium under metal stress conditions, with intracellular DA concentrations decreasing relative to nonstressed cells. Fe uptake rates by P. multiseries were slow compared to other marine diatoms in the absence of dissolved DA but were enhanced threefold (P < 0.03) by adding DA to the medium. DA addition also partially alleviated toxic Cu conditions. Our findings suggest that DA production during exponential growth of these two toxigenic Pseudo-nitzschia species is directly induced by Fe-deficient or Cu stress conditions and that 95% of this DA is actively released into the medium. Changing trace metal conditions in coastal waters therefore may have a profound effect upon intracellular DA concentrations and thereby influence the toxic effect of these harmful bloom events.

Manipulation of iron availability in nearshore waters is discussed with the presentation of results of natural population incubation experiments from costal upwelling waters off the California coast in which the fungal siderophore desferriferrioxime B (DFB) was added to cut down iron assimilation. Findings show that DFB can be used to manipulate biologically accessible iron to find out how iron affects community structure of algae and carbon cycling in waters replete with iron.

An investigation of the iron (Fe) perturbations needed to stimulate diatom production requires an assessment of the lowest Fe concentration whereby uptake still allows maximum cellular growth rates and of what Fe flux to surface waters is then required to sustain high diatom productivity once the concentration threshold is exceeded. Research in this area has concluded that climate forcing has definitely had an impact on productivity in the eastern equatorial Pacific. Furthermore, equatorial sediment records give an insight into these impacts. However, some element of this cycling may have been fuelled by localized tectonic processes in the Papua New Guinea island-arc area.

The stability of human prion protein (PrP) from its normal cellular form (denoted [PrP.sup.C]) with pH is examined to understand the significantly reduced stability in the [PrP.sup.C] by the protonation of two histidine residues, His187 and His155. The protonation state of H187 appears to be crucial for determining the conformation of PrP and are relevant to the pathogenic H187R mutation found in humans, which is associated with an inherited prion disease [also termed Gerstmann-Straussler-Scheinker (GSS) syndrome] with unusual features such as childhood neuropsychiatric illness.

Marine colloids are abundant in the oceans representing 30-50% of the dissolved organic carbon. There is a lack of consensus about the processes that regulate colloid cycling. Chin and colleagues have invoked a polymer gel theory to explain the behaviour of marine colloids. They show the significance of nonspecific surface interactions in colloid cycling and have discovered that discrete natural polymers coalesce spontaneously, forming large, sinking conglomerates. Particulate gels were found to re-form from soluble and colloidal precursors, after the removal of previous gels via filtration.

Four hundred and eighty kilograms of iron was introduced in the Pacific Ocean, 500 kilometers south of Galapagos Islands, to investigate the influence of iron on biomass and phytoplankton production. The region near Galapagos islands consists of abundant supply of plant nutrients. The investigation reveals that the concentration of iron in these regions does not influence biomass and phytoplankton production.